Knit fabric and an article comprising same

ABSTRACT

A knit fabric suitable as a reinforcement for elastomeric articles comprises a plurality of reinforcement yarns wherein each course of the fabric comprises either a first or second yarn, the modulus of the first yarn being different from the modulus of the second yarn, and the courses comprising the first and second yarns are arranged in one of the following sequences, (a) alternating courses comprise first and second yarns respectively, (b) the courses form a repeat pattern of, in order, a course comprising a first yarn, two courses comprising a second yarn and a course comprising a first yarn or (c) the courses form a repeat pattern of, in order, a course comprising a second yarn, two courses comprising a first yarn and a course comprising a second yarn.

BACKGROUND

1. Field of the Invention

This invention relates to knitted reinforcement structures used forpressed or molded articles such as hoses for fluid conveyance.

2. Description of Related Art

U.S. Pat. No. 7,572,745 to Branch et al discloses an improved yarn for aknit reinforcement in a flexible hose. The flexible hose according tothe invention may comprise a tube, a knit fabric, and a cover whereinsaid knit fabric comprises a hybrid yarn comprising a first yarn ofco-para-aramid fibers and a second yarn of meta-aramid fibers. Theco-para-aramid and meta-aramid yarns may be twisted, plied, folded, orcommingled together to form a single hybrid reinforcing yarn for thehose. The knit fabric may reside between a tube and a cover and/or maybe embedded in a layer of the hose. One or more layers of a knit fabricof hybrid yarn may be the primary reinforcing member of a hose.

PCT publication number WO2010/131216 to Mezzalira et al describes aflexible hose comprising, as viewed from the inside, at least one firstinner layer made of a first thermoplastic polymer material, at least onereinforcement layer composed of a plurality of yarns knitted together toform a plurality of stitches of tricot type, and at least one secondlayer made of a second thermoplastic polymer material. At least onefirst yarn of said yarns that form said at least one reinforcement layeris a high tenacity fiber and at least one second yarn is a polyesterfiber yarn or the like interwoven with the first yarn. A method ofmaking such hose is also described.

PCT publication number WO2012/000713 to Brettschneider et al describesan article composed of a polymeric material which has been provided withan embedded reinforcement which consists wholly or partly of a textilematerial, characterized in that, in a first reinforcement variant, thetextile material consists exclusively of polyoxadiazole (POD) and/or aPOD derivative and/or a POD copolymer, or, in a second reinforcementvariant, the textile material is a textile material combinationconsisting of POD and/or a POD derivative and/or a POD copolymer, and ofat least one further textile material which is not part of theaforementioned POD group, or, in a third reinforcement variant, thetextile material comprises a material combination consisting of PODand/or a POD derivative and/or a POD copolymer and at least one furthermaterial which is not part of any textile group. The article is moreparticularly a hose, more particularly again a charge-air hose,consisting of an inner layer and an outer layer of a polymeric materialand an embedded reinforcement, for example in the form of a POD knit.

There is an ongoing need to provide knitted fabrics of improvedmechanical strength that can enhance the properties of articlescomprising the fabric, for example to increase the pressure carryingcapability of a rubber hose.

SUMMARY OF THE INVENTION

This invention pertains to a knit fabric suitable as a reinforcement fortubular elastomeric articles comprising a plurality of first and secondreinforcement yarns wherein,

-   -   (a) each course of the fabric comprises either a first or second        yarn, the yarns having a tenacity of at least 2.2 g/dtex,    -   (b) the modulus of the first yarn is different from the modulus        of the second yarn, and    -   (c) the courses comprising the first and second yarns are        arranged in one of the following sequences,        -   (i) alternating courses comprise first and second yarns            respectively,        -   (ii) the courses form a repeat pattern of, in order, a            course comprising a first yarn, two courses comprising a            second yarn and a course comprising a first yarn,        -   (iii) the courses form a repeat pattern of, in order, a            course comprising a second yarn, two courses comprising a            first yarn and a course comprising a second yarn.

The invention also pertains to an article comprising the knit fabric.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of part of a prior art knit fabric.

FIG. 2 shows one embodiment of a knit fabric of this invention.

FIG. 3 shows another embodiment of a knit fabric of this invention.

FIG. 4 shows yet another embodiment of a knit fabric of this invention.

FIG. 5 shows a further embodiment of a knit fabric of this invention.

FIG. 6 is a schematic of a hose comprising a knit fabric of thisinvention.

DETAILED DESCRIPTION

Fabric

This invention pertains to a knit fabric. Knitting is the interloopingof yarn feedstock into vertical columns called wales and horizontal rowsof loops called courses with fabric coming out of the machine in thewales direction.

In some embodiments, each course of the fabric comprise either a firstreinforcing yarn or a second reinforcing yarn. The courses of first andsecond yarns are arranged in one of the following sequences (i)alternating courses comprise first and second yarns respectively, (ii)the courses form a repeat pattern of, in order, a course comprising afirst yarn, two courses comprising a second yarn and a course comprisingcomprising a first yarn or (iii) the courses form a repeat pattern of,in order, a course comprising a second yarn, two courses comprising afirst yarn and a course comprising a second yarn. This may be furtherexplained by reference to the Figures.

FIG. 1 shows a section of a prior art knitted fabric 10. Wales areindicated by the vertical orientation arrow “a” and courses byhorizontal orientation arrow “b”. The yarns 11 of this fabric are allthe same and are either yarns of a single material or are blended(hybrid) yarns formed by twisting together at least two different yarnsinto a single hybrid yarn.

FIG. 2 shows a section of one embodiment of this invention 20 comprisingalternating courses of first yarns 21 and second yarns 22 respectively.FIG. 3 shows a section of another embodiment of this invention 30 inwhich the courses form a repeat pattern of, in order, a coursecomprising a first yarn 21, two courses comprising a second yarn 22 anda course comprising comprising a first yarn 21. FIG. 4 shows a sectionof yet another embodiment of this invention 40 in which the courses forma repeat pattern of, in order, a course comprising a second yarn 22, twocourses comprising a first yarn 21 and a course comprising comprising asecond yarn 22.

In some embodiments, the knit fabric comprises at least three differentreinforcement yarns wherein, no more than two successive courses of thefabric comprise the same yarn. By “same yarn” is meant yarn of the samecomposition and having the same physical properties. An example of thisis shown at 50 in FIG. 5 which shows five courses of a section of a knitfabric comprising in order a course of first yarns 22, followed by twocourses of second yarns 21, a course of third yarns 23 and a course offirst yarns 22.

Yarns

The first, second and third reinforcing yarns comprise fibers orfilaments having a tenacity of at least 2.2 g/dtex (2 g/denier). Thefilaments of the yarns may be polymeric or inorganic. Preferably thefilaments are continuous. Multifilament yarn spun onto a bobbin in apackage contains a plurality of continuous filaments. The multifilamentyarn can be cut into staple fibers and made into a spun staple yarnsuitable for use in the present invention. The staple fiber can have alength of about 1.5 to about 5 inches (about 3.8 cm to about 12.7 cm).Another form of suitable yarn is stretch-broken yarn in which filamentshaving a length of from 2 to about 80 inches (about 5 cm to about 200cm) are spun and twisted together to form single end yarns having adenier in the range of from 100 to 10,000 denier (111 to 11,000 dtex).

In the case of a fabric comprising only first and second yarns, thefilaments of the first and second yarns may be of a differentcomposition or the yarns may be of the same composition but havedifferent moduli. An example of the first type is a first yarn ofp-aramid such as Kevlar® and a second yarn of m-aramid such as Nomex®.An example of the second type is a fabric where the first and secondyarns are both para-aramid yarns, but the first yarn is a standardmodulus yarn such as Kevlar®29 and the second yarn is an intermediatemodulus yarn such as Kevlar®49.

In the case of a fabric comprising first, second and third reinforcingyarns, the filaments of the first, second or third yarns may be ofdifferent composition. For example, the first yarn may be p-aramid, thesecond yarn may be m-aramid and the third yarn may be nylon or the firstyarn may be p-aramid, the second yarn may be glass and the third yarnmay be polyester. In some other embodiments, two of the yarns may be ofthe same composition but of different moduli and the third yarn is of adifferent composition from the first and second yarns. In yet anotherembodiment, the filaments of the first, second and third yarns may be ofthe same composition but all three yarns have different moduli asexemplified by standard, intermediate and high modulus carbon fibers.

The filaments comprising the first, second or third yarns may bearomatic polyamide, aromatic copolyamide, aliphatic polyamide, glass,carbon, polyester, polyazole, polyolefin or cellulose. Examples ofaromatic polyamides are meta-aramid such as Nomex® and para-aramid suchas Kevlar®. Aliphatic polyamides include a range of nylon materials suchas nylon 6,6.

Another suitable fiber is one based on aromatic copolyamide prepared byreaction of terephthaloyl chloride (TPA) with a 50/50 mole ratio ofp-phenylene diamine (PPD) and 3,4′-diaminodiphenyl ether (DPE). Yetanother suitable fiber is that formed by polycondensation reaction oftwo diamines, p-phenylene diamine and 5-amino-2-(p-aminophenyl)benzimidazole with terephthalic acid or anhydrides or acid chloridederivatives of these monomers.

Glass fibers include “E” glass and “S” Glass. E-Glass is a commerciallyavailable low alkali glass. One typical composition consists of 54weight % SiO₂, 14 weight % Al₂O₃, 22 weight % CaO/MgO, 10 weight % B₂O₃and less then 2 weight % Na₂O/K₂O. Some other materials may also bepresent at impurity levels S-Glass is a commercially availablemagnesia-alumina-silicate glass. This composition is stiffer, strongerand more expensive than E-glass and is commonly used in polymer matrixcomposites.

An example of polyester is polyethylene terephthalate (PET).

Examples of cellulosic fiber are cotton, cellulose acetate, andregenerated cellulose fibers known as rayon.

Article

The knit fabric of this invention may be used as a reinforcement forpolymeric or elastomeric articles.

Examples of elastomeric articles include tires and hoses. The fabric maybe used as a load carrying component in the carcass of a tire. FIG. 6depicts a schematic of a hose comprising a knit fabric of the presentinvention. The hose is shown generally at 60. The first component is acore tube (61) having a circumferential inner surface whichconventionally contacts a fluid or gas and an opposing circumferentialouter tube surface. The materials suitable for core tube (61) areelastomeric and are well known in the art. Suitable examples includehydrogenated nitrile rubber, silicone rubber, fluorosilicone rubber,methylphenylsilicone rubber, natural rubber, EPDM, CPE and acrylicrubber. EPDM means ethylene propylene diene monomer rubber; CPE meanschlorinated polyethylene. It is understood the elastomeric materialwhich is chosen will be dependent on the final use of the hose.Illustratively, if a corrosive substance is to be transported throughthe hose, the elastomeric material is chosen to withstand suchcorrosion. The knit fabric reinforcement layer (62) surrounds the outersurface of the core tube. An elastomeric layer (63) surrounds thereinforcement layer (62) on its outer surface. The type of elastomer canbe the same or different relative to the core (61). It is understoodthat various constructions may be employed. Illustratively, more thantwo reinforcement layers (62) can be utilized. Furthermore, the coretube (61) can be lined on its inner surface with a fluorocarbon-basedmaterial which will contact the fluid or gas to be transported. Suitableexamples of such lining materials include poly(tetrafluoroethylene) andperfluoroalkoxy polymer.

Another example of the use of the knit fabric is a polymeric compositecomprising the knit reinforcement and a matrix resin which may bethermoplastic or thermoset. Typically, the fabric comprises from 25 to55 weight percent of the weight of fabric plus matrix. In someembodiments the fabric comprises from 30 to 45 weight percent of theweight of fabric plus matrix. Exemplary thermoset matrix resins areepoxy, phenolic, polyester, bismaleimide and cyanate ester. Exemplarythermoplastic resins are polyetheretherkenone (PEEK),polyetherketoneketone (PEKK), polyethersulfone (PES), polyarylsulfone(PAS), polyethylene and polypropylene.

EXAMPLES

In the following examples:

Y1 is a para-aramid yarn available under the tradename Kevlar® 29 fromE.I. du Pont de Nemours and Company, Wilmington, Del. (DuPont) having anominal tenacity of 25.5 g/den and a nominal modulus of 76 GPa. Thenominal linear density is 1000 denier.

Y2 is a para-aramid yarn available under the tradename Kevlar® 49 fromDuPont having a nominal tenacity of 25.5 g/den and a nominal modulus of117 GPa. The nominal linear density is 1420 denier.

Y3 is a meta-aramid yarn available under the tradename Nomex® 430 fromDuPont having a nominal tenacity of 5.0 g/den and a nominal modulus of12.7 GPa.

Y4 is a 6K carbon fiber yarn available under the tradename HexTow® AS4from Hexcel Corporation, Stamford, Conn. (Hexcel) having a nominaltensile strength 4330 MPa and a nominal tensile modulus of 231 GPa.

Y5 is a 6K carbon fiber yarn available under the tradename HexTow® IM7from Hexcel having a nominal tensile strength 5310 MPa and a nominaltensile modulus of 276 GPa.

Y6 is a 12K carbon fiber yarn available under the tradename HexTow® IM10from Hexcel having a nominal tensile strength 6964 MPa and a nominaltensile modulus of 303 GPa.

The knitted reinforcement can be made on a Harry Lucas RRU—2×4s modelnumber 5594 knitting machine available from Knitting Machine & SupplyCo., Inc. Clark, N.J. This machine is designed for knitting a coveraround a rubber tube and can be built with up to 6 cam tracks forlock/skip stitch patterns and 4-12 feed packages for supply filamentelements and textile yarns.The fabric style is of the type known in the trade as jersey or terryknit, also known in the hose trade as a plain stitch. The knit couldalso be of a lock or skip stitch.

The following examples are given to illustrate the invention and shouldnot be interpreted as limiting it in any way. Examples preparedaccording to the process or processes of the current invention areindicated by numerical values. Control or Comparative Examples areindicated by letters.

Comparative Example A

Example A is prepared solely from yarns Y3. The knit fabric has the sameyarn in every course.

Comparative Example B

Example B is prepared solely from yarns Y1. The knit fabric has the sameyarn in every course.

Comparative Example C

Example C is prepared solely from yarns Y4. The knit fabric has the sameyarn in every course.

Example 1

Example 1 is prepared from yarns Y1 (first yarn) and Y2 (second yarn).The knit fabric has alternating courses of yarns Y1 and Y2.

Example 2

Example 2 is prepared from yarns Y1 (first yarn) and Y3 (second yarn).The knit fabric has alternating courses of yarns Y1 and Y3.

Example 3

Example 3 is prepared from yarns Y1 (first yarn) and Y2 (second yarn).The courses of the knit fabric form a repeat pattern of, in order, acourse comprising a first yarn (Y1), two courses comprising a secondyarn (Y2) and a course comprising a first yarn (Y1).

Example 4

Example 4 is prepared from yarns Y1 (first yarn) and Y3 (second yarn).The courses of the knit fabric form a repeat pattern of, in order, acourse comprising a second yarn (Y3), two courses comprising a firstyarn (Y1) and a course comprising a second yarn (Y3).

Example 5

Example 5 is prepared from yarns Y4 (first yarn), Y5 (second yarn) andY6 (third yarn). The courses of the knit fabric form a repeat patternof, in order, a course of first yarns (Y4), followed by two courses ofsecond yarns (Y5), a course of third yarns (Y6) and a course of firstyarns (Y4).

Example 6

A hose is made by the extrusion of uncured ethylene propylene diamine(EPDM) compound as an annular tube of circular cross-section and ofsignificantly greater length than diameter. The EPDM compound may be ofthe type typically used for long life or standard coolant or heater hoseapplications. The tube is then covered with a knit, formed by amulti-feed circular knitter such as by a Harry Lucas RRU machine. Thestaging of the feed bobbins or supply bobbins for the forming knit isdescribed in Example 2, in which a plain knit is formed with alternatingcourses of yarn types by the alternating location of feed packages onthe knitter deck. In this instance, an 8 feed knitter is used, such that4 packages of Y1 and 4 packages of Y2 are placed in a regularalternating pattern on the knitter deck. The knitter places 10 courseper inch along the length of the hose and uses 16 needles to form theplain stitch. The tube with knitted yarn is then passed through anannular extrusion die that applies a cover layer of extended EPDMcompound as the ‘cover layer’ to protect the knit from damage and toprovide body to the overall hose structure. EPDM compound informationcan be found in trade literature such as the RT Vanderbilt RubberHandbook 13^(th) edition, 1990. The assembly is then cut to lengths andformed over steel or aluminum mandrels to be molded into the desiredshape during cure in steam at 150 C for 15 minutes. The cured rubberhoses are then removed from the mandrels after cooling and subsequentlycleaned, trimmed, and tested for commercial sale.

Example 7

A hose is made by the extrusion of uncured silicone compound (VMQ) as anannular tube of circular cross-section and of significantly greaterlength than diameter. The VMQ compound may be of the type typically usedfor long life or standard turbocharger or charge-air hose applications.The tube is then covered with a knit, formed by a multi-feed circularknitter such as by a Harry Lucas RRU machine. The staging of the feedbobbins or supply bobbins for the forming knit is described in Example5, in which a plain knit is formed with alternating courses of yarntypes by the alternating location of feed packages on the knitter deck.In this instance, a 12 feed knitter is used, such that 4 packages of Y4,4 packages of Y5, and 4 packages of Y6 are placed in a regularalternating pattern on the knitter deck. For further illustration theyarn packages would form the following pattern repeated 4 times: Y4 Y5Y6. The knitter places 6 course per inch along the length of the hoseand uses 36 needles to form the plain stitch. The tube with knitted yarnis then passed through an annular extrusion die that applies a coverlayer of VMQ compound as the ‘cover layer’ to protect the knit fromdamage and to provide body to the overall hose structure. VMQ compoundinformation can be found in trade literature such as the RT VanderbiltRubber Handbook 13^(th) ed 1990. The assembly is then cut to lengths andformed over steel or aluminum mandrels to be molded into the desiredshape during cure in steam at 150 C for 15 minutes. The cured rubberhoses are then removed from the mandrels after cooling and subsequentlycleaned, trimmed, and tested for commercial sale.

When tested in a loop to loop test, the elongation at break of a knitstructure as described above comprising at least two different yarns isgreater than the elongation at break of the stiffest yarn of the atleast two different yarns and the knit structure has a strength greaterthan that of a knit comprised solely of the most compliant yarn of theat least two different yarns. When such a knit is built into a hose thiswill deliver improved pressure performance for volumetric expansion.

What is claimed is:
 1. A knit fabric comprising a plurality of first andsecond reinforcement yarns wherein, (a) each course of the fabriccomprises either a first or second yarn, the yarns having a tenacity ofat least 2.2 g/dtex, (b) the modulus of the first yarn is different fromthe modulus of the second yarn, and (c) the courses comprising the firstand second yarns are arranged in sequences selected from the groupconsisting of (i) alternating courses comprising first and second yarnsrespectively, (ii) a repeating pattern of courses forming, in order, acourse comprising a first yarn, two courses comprising a second yarn anda course comprising a first yarn, (iii) a repeating pattern of coursesforming, in order, a course comprising a second yarn, two coursescomprising a first yarn and a course comprising a second yarn, andwherein the fabric is a reinforcing component of a tubular elastomericarticle, a tire or a composite structure.
 2. The fabric of claim 1,wherein the first and second yarns comprise filaments of the samepolymer.
 3. The fabric of claim 1 wherein, the first yarn comprisesfilaments of a different polymer from the polymer of the filaments ofthe second yarn.
 4. The fabric of claim 3, wherein the polymer of thefilaments of the first yarn is m-aramid and the polymer of the filamentsof the second yarn is p-aramid.
 5. A hose comprising the knitted fabricof claim
 1. 6. A tire comprising the knitted fabric of claim
 1. 7. Afiber reinforced composite structure comprising the knitted fabric ofclaim 1.